Process for the production of alpha-naphthyl esters

ABSTRACT

A PROCESS FOR THE PRODUCTION OF ALPHA-NAPHTHYL ESTERS OF ALIPHATIC CARBOXYLIC ACIDSS HAVING FROM 1 TO 4 CARBON ATOMS WHICH COMPRISES SUBJECTING NAPHTHALENE TO OXIDATION IN THE PRESENCE OF SAID ALIPHATIC CARBOXYLIC ACIDS AND A COBALT SALT CAPABLE OF FORMING COBALTIC IONS IN A RATIO SUCH THAT 2X-A IS BETWEEN 0.2 AND 1.5, X AND A BEING RESPECTIVELY THE MOLARITY OF THE COBALIC IONS AND OF SAID COBALT SALT IN THE REACTION MIXTURE, AT A TEMPERATURE FROM 20 TO 150*C. AND IN THE ABSENCE OF OXYGEN.

United States Patent Oflice 3,809,715 Patented May 7, 1974 3,809,715 PROCESS FOR THE PRODUCTION OF ALPHA-NAPHTHYL ESTERS Jacques Daniel Victor Hanotier and Monique Josephe Simone Hanotier, Brussels, Belgium, assignors to Labofina S.A., Brussels, Belgium No Drawing. Filed Nov. 13, 1972, Ser. No. 306,041 Int. Cl. C07c 69/14, 39/14, 69/24 US. Cl. 260-479 R 7 Claims ABSTRACT OF THE DISCLOSURE A process for the production of alpha-naphthyl esters of aliphatic carboxylic acids having from 1 to 4 carbon atoms which comprises subjecting naphthalene to oxidation in the presence of said aliphatic carboxylic acids and a cobalt salt capable of forming cobaltic ions in a ratio such that 2xA is between 0.2 and 1.5, x and A being respectively the molarity of the cobaltic ions and of said cobalt salt in the reaction mixture, at a temperature from 20 to 150 C. and in the absence of oxygen.

The present invention relates to a process for the production of alpha-naphthyl esters of aliphatic monocarboxylic acids by oxidation of naphthalene.

The alpha-naphthyl esters may be readily hydrolyzed into alpha-naphthol, which is used primarily for the manufacture of coloring substances, synthetic perfumes and insecticides, such as alpha-naphthyl-N-methylcarbamate. For some of these uses, the alpha-naphthol must be very pure and more particularly, it must be practically free from the beta-naphthol isomer. It is practically impossiblev to separate the alpha and beta isomers by known methods. Consequently, long and costly synthesis methods are used in order to produce alpha-naphthol which is practically free from the beta-isomer. According to one of the known processes for producing the alpha-naphthol, naphthalene is nitrated under carefully controlled conditions in order to avoid the joint formation of dinitrated derivatives. The nitronaphthalene is then hydrogenated into naphthylamine, the alpha and beta isomers (in a ratio of about 8: l) are separated and the alpha-naphthylamine is hydrolyzed by sufuric acid at elevated pressure and temperature. In addition, the known processes for the direct oxidation of naphthalene give very low yields of alpha-naphthol. Usually, these known methods of oxidizing naphthalene produces naphthoquinone or results in a ring breakdown with formation of phthalic acid. Therefore, it appears that a new and improved method for the effective conversion of naphthalene into alpha-naphthol, practically free from beta-naphthol, would be most useful.

An object of the present invention is to provide a new and novel process for the direct oxidation of naphthalene into a precurser of alpha-naphthol. Another object of the present invention is to provide a new and novel process for the direct oxidation of naphthalene to produce the alpha-naphthyl ester of an aliphatic carboxylic acid which will produce alpha-naphthyl in substantially pure form by hydrolysis. Still another object of the present invention is to provide a new and novel process for the direct oxidation of naphthalene into an alpha-naphthyl ester, without formation of beta-naphthyl ester. Additional objects will become apparent from the following description of the invention herein disclosed.

The present invention, which fulfills these and other objects, is a process for the production of an alphanaphthyl ester of an aliphatic monocarboxylic acid having from 1 to 4 carbon atoms, said process comprising oxidizing naphthalene in the presence of said aliphatic carboxylic acid with a cobalt salt containing cobaltic ions in a ratio such that 2xA is between 0.2 and 1.5, x and A being respectively the molarity of the cobaltic ions and of said cobalt salt in the reaction mixture, at a temperature from 20 to 150 C. and in the absence of molecular oxygen.

The cobalt salt used in the process of the present invention may be any cobalt salt having a solubility in the reaction mixture which is enough so that the required concentration is obtained. Cobalt salts of aliphatic monocarboxylic acids containing from 1 to 4 carbon atoms are particularly useful. For example, such cobalt salts as those of acetic and propionic acid are useful. Generally, the acid of the cobalt salt is the same as the acid producing the ester substituent of the alpha-naphthyl ester.

It has been found quite unexpectedly that the conversion of naphthalene to the alpha-naphthyl ester takes place only when the molarity A of the cobalt salt and the molarity x of the cobaltic ions are such that 2xA is at least 0.2. To achieve this, the cobalt salt must be used in a concentration of at least 0.2 when it is entirely a cobaltic salt. However, a high concentration of cobaltic ions is not enough by itself to secure and effective oxidation when the total concentration of cobalt is too high. The activity of the cobaltic ions is drastically reduced when 2xA is lower than 0.2, even when A is high, and the activity is practically negligible when 2xA=0. Consequently, 2xA may be considered as being the concentration of active cobaltic species or of active Co(III) and will be referred to hereinafter as active Co(III).

In the presence of active Co(III) at the concentrations hereinabove defined, naphthalene is oxidized at temperatures not higher than 150 C., most often between 20 and 150 C. The preferred oxidation temperature is between 40 and C. Generally, the reaction rate increases when the temperature is increased, but the selectivity toward the formation of alpha-naphthyl ester is lowered. Therefore, for best results, the temperature is generally kept below 120 C. The pressures at which the reaction is carried out generally are approximately atmospheric though superatmospheric pressures may be employed if desired.

The reaction rate may be increased by adding to the reaction mixture a relatively strong inorganic or organic acid, preferably such an acid having a dissociation constant K higher than 5.10- This acid must be soluble in the reaction mixture and not interfere with the reaction. For example, trifluoroacetic acid (K=6.10- trichloro- -acetic acid (K=2.10" phosphoric acid (K'=7.5.10-

may be used. However, acids such as hydrochloric acid, hydrobromic acid, hydroiodic acid and nitric acid, interfere with the reaction and should be avoided.

In order to obtain an effective and selective oxidation of naphthalene into alpha-naphthyl ester according to the process of this invention, the reaction must be carried out in the absence of molecular oxygen, for example in an atmosphere of nitrogen or any other inert gas.

The invention will be further described with reference to the following examples which are given only for purposes of illustration, and are not intended to limit the scope of said invention.

EXAMPLE 1 A solution containing 0.20 M by liter of naphthalene and 0.52 M by liter of cobaltic acetate in acetic acid was maintained for 3 hours at 30 C. under nitrogen atmosphere. The ratio of cobaltic ions to total cobalt ions in this solution was initially 0.95 so that the concentration of active cobalt (III) was 0.47 atom-gram per liter.

At the end of the 3 hour period, unreacted cobaltic ions were reduced by addition of a concentrated aqueous solution of ferrous ions. The resulting mixture was then diluted with ether and neutralized with solid sodium carbonate until no more evolution of carbon dioxide could be noticed. The resulting ether solution was then analyzed by vapor-phase chromatography. It was determined that 10.4% of the starting naphthalene had been transformed into alpha-naphthyl acetate. Only traces of beta-naphthyl acetate could be detected.

EXAMPLE 2 The procedure of Example 1 was again followed except that the reaction was carried out for only one hour at a temperature of 50 C. instead of 30 C. By the same procedure as described above, it was determined that 22.2% of the starting naphthalene had been transformed into alpha-naphthyl acetate with a selectivity of nearly 100%.

EXAMPLE 3 The procedure of Example 1 was again followed except that the reaction was carried out for only minutes at a temperature of 100 C. It was determined that under these conditions 19% of the starting naphthalene had been transformed into alpha-naphthyl acetate. Betanaphthyl acetate could not be practically detected.

EXAMPLE 4 The procedure of Example 2 was again followed except that cobaltic propionate was employed as oxidizing agent and propionic acid employed as solvent. The starting naphthalene is transformed almost exclusively into alphanaphthy propionate.

EXAMPLE 5 naphthyl acetate. As in the preceding examples, only traces of the beta-isomers could be detected.

By comparing these results with those of Example 1, it appears clearly that strong acids such as trifluoroacetic acid have a promoting effect on the rate of the reaction without altering its selectivity.

We claim:

1. A process for the production of an alpha-naphthyl ester of an aliphatic carboxylic acid having from 1 to 4 carbon atoms which comprises contacting naphthalene with an aliphatic carboxylic acid and a cobalt salt capable of forming cobaltic ions in a ratio such that 2xA is between 0.2 and 1.5, x and A being respectively the molarity of the cobaltic ions and of said cobalt salt in the reaction mixture, at a temperature from 20 to 150 C. and in the absence of oxygen.

2. The process of claim 1 wherein the cobalt salt is the cobalt salt of an aliphatic monocarboxylic acid containing from 1 to 4 carbon atoms.

3. The process of claim 1 wherein the reaction is carried out in the presence of a strong acid having a dissociation constant higher than 5.10

4. The process of claim 1 wherein the reaction is carried out at a temperature between 40 and C.

5. The process of claim 3 wherein said strong acid is trifluoroacetic acid.

6. The process of claim 1 wherein said cobalt salt is the salt of an aliphatic monocarboxylic acid containing 1 to 4 carbon atoms.

7. The process of claim 6 wherein said cobalt salt is cobalt acetate.

References Cited UNITED STATES PATENTS 3,649,675 3/1972 Kochl 260-488 JAMES A. PATTEN, Primary Examiner U.S. Cl. X.R. 260-62l G UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 59809,,715 Dat d y 197A Inventods) Jacques Daniel Victor et a1.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the Title Page, in the heading, after "Ser. No. 506,0hl"

-- Claims Priority, application France, J l 6 1972 Signed and sealed this 1st day of April 1975.

(vr I, v j i t t 9 S t C MARSHALL DAN-N nUTZ-I C. ZUISON Commissioner of Patents attesting Officer and Trademarks FORM POJOSO (1069) USCOIMM-DC 603164 6? uIs. covnmutm' rnmrmo omcz: 93 o 

